Answer:
x= -18
Explanation:
Replace the term "a number" with x, since you don't know the number. It makes it easier to understand. Now set up your problem as the question says.
It becomes 5x-18-4x=-36. Decreased means the same thing as minus, it's just there to confuse you. Now do basic algebra. Combine like terms, so 5x-4x becomes just x. Add the -18 to the other side, so 18-36=-18. So x=-18. When a positive number is subtracting a negative number larger than itself, sometimes it's easier to think of it as 36-18 instead of 18-36 to get the right number, and then just add the negative sign after. Hope this helps!